Rechargeable batteries (“stacks”) are known, which are used to supply power to an electric load in case, for example, there is an unexpected interruption of the supply of power or, in general, for back-up applications. Furthermore, these batteries are charged by means of the energy released during the braking of the vehicle.
Document U.S. Pat. No. 6,265,851 describes a system to move a trolley for the transportation of electronic material on a monorail track. This power supply system comprises batteries and ultracapacitors, which are connected to a switch. The motor of the electric trolley is alternatively supplied with power by the ultracapacitors or by the batteries or by both, depending on the energy needed by the motor and by the residual energy that can be delivered by the ultracapacitors and the batteries. The ultracapacitors are the primary source of power and the batteries are used as auxiliary or secondary source of power. The batteries are used during acceleration steps and when a surplus of energy is needed.
The applicant found out that the exchange of energy enabled by ultracapacitors is characterized by high peak powers (around hundreds of kW, in the railway field) for relative short times (approximately 10 seconds). The system according to U.S. Pat. No. 6,265,851 cannot be used in the railway field for the purpose of supplying power to the vehicle while it is running, because the ultracapacitor runs down too quickly and with very high peak powers.
Document EP 2306610 relates to a system to generate, store and transmit energy in an area, wherein an electrical network comprises two different energy storage means, in particular batteries and supercapacitors. This electrical network extends over a given area in order to transport electrical energy and has nothing to do with transportation by means of trains or trams with overhead wires.
Document WO 2007/082168 describes a method and a system comprising one or more supercapacitors and one or more batteries. The supercapacitors are charged by means of energy coming from a generic source of energy and the electrical energy stored in them is used both to charge the batteries and to supply power to an electrical load. In this case, again, as already mentioned when discussing document EP 2306610, the system is used to store and transport energy in an area and it has nothing to do with the use of energy in a vehicle for trams with overhead wires.